Reasons to Believe

Ancient Muds Bog Down Evolutionary Explanation for Life’s Origin

When I was a kid, I played a lot of sandlot football. And nothing was more fun than playing football after a hard rain on a muddy field. It was a blast to slosh around in the mud. But if the field was too muddy, it was hard to run, making it difficult to advance the ball down the field.

Scientists like playing in the mud, too. And recently, a scientist from the University of Washington had a good time working with ancient mud from early Earth (dating to 3.8 billion years in age). As a result of her efforts, Eva Stüeken now argues that the nitrogen in some of the oldest muddy sediments on Earth was produced by microorganisms.

Her interpretation of the nitrogen in ancient muds adds to the mounting evidence for an early and rapid origin of life, making it more difficult for the scientific community to advance an evolutionary explanation for life’s start.1

In earlier studies, geochemists measured about 430 parts per million (ppm) nitrogen in biotite minerals recovered from 3.8-billion-year-old sediments of the Isua Formation of Greenland. Typically, the highest levels of nitrogen co-occur with graphite granules. (Some geochemists regard the graphite granules as a biomarker.) Because nitrogen is an integral component of biomolecules such as DNA and proteins, the occurrence of this element in the biotite can be taken as a biosignature.

Unfortunately, it is not that straightforward. Some geochemists claim that the nitrogen in the ancient mud comes from abiotic sources. For example, lightning and volcanism can fix atmospheric nitrogen, conceivably accounting for its presence in the biotite grains.

To test this idea, University of Washington earth scientist Eva Stüeken modeled the amount of abiotic nitrogen that would be expected in ancient muds if it came exclusively from abiotic processes. She determined that abiotic pathways were insufficient to explain nitrogen levels, meaning that some of the nitrogen must be biogenic.

Early Life on Earth

The presence of nitrogen in ancient muds adds to the mounting geochemical and fossil evidence that points to the presence of life on early Earth. (See the Resources section below to learn about other evidences for early life on Earth.) It looks like life appeared on Earth as soon as our planet could sustain it. In fact, a case can be made that life could not have originated and persisted on Earth prior to 3.8 billion years ago. This constraint means that life must have originated within a geological instant.

Both the geochemical and fossil evidence indicate that Earth’s first life was microbial in nature. Though morphologically simple, the geochemical data indicates that this life was biochemically diverse and complex. There are good reasons to think that the first life-forms could engage in a wide range of metabolic activities, including photosynthesis, methanogenesis, methanotrophism, and sulfur disproportionation. While far from conclusive, the biogenic nitrogen in the ancient muds suggests that Earth’s first life also had the capacity to fix nitrogen.

Evidence for Evolution or Creation?

As discussed in Origins of Life, the sudden, early appearance of metabolically sophisticated life on Earth is difficult to accommodate within an evolutionary framework. Traditionally, origin-of-life researchers have maintained that the origin-of-life process would have required hundreds of millions of years—maybe even a billion years. To put it another way, when viewed from an evolutionary standpoint, no one would have expected that lifes origin would have happened so rapidly.

This latest insight about the ancient muds creates an additional problem for evolutionary models. It argues against the existence of a prebiotic soup on early Earth. This idea is a cornerstone for most origin-of-life models. According to this idea, life emerged on early Earth out of a prebiotic soup—a complex chemical mixture—as the molecules in the soup became more complex and, eventually, self-organized into the first cellular entities.

If a prebiotic soup existed on Earth, it should leave behind a geochemical signature in the oldest rocks on Earth. Geochemists have uncovered chemical residues in the oldest rock formations on Earth—including the nitrogen in the ancient muds—but inevitably, these residues turn out to be biogenic in origin, not abiotic. In other words, there is no geochemical evidence for a prebiotic soup. This idea is all covered with the mud.

On the other hand, the sudden appearance of biochemically complex life on early Earth bears the signature of the Creator’s handiwork. They are also key predictions for the RTB model for life’s origin.

Resources

Endnotes

  1. Eva Stüeken, “Nitrogen in Ancient Mud: A Biosignature?,” Astrobiology 16 (September 2016): 730–35, doi:10.1089/ast.2016.1478.

Subjects: Origin of Life